Because, why not? Small testing fix I saw when scanning the code.

After seeing you post this on twitter I checked it out and enjoyed it. I'm working on doing a talk on unit testing and love this kind of stuff. This is so much better than contrived examples that test 1+1 = 2. 

Anyway, I saw a couple things when looking at it and since I love github so much, I decided to do a pull request instead of a tweet telling you. :)

- Fixed Test in a context that said it was testing the initializer but it was checking the class method still.
- Removed the redundant [super initialize] call in your main AFImageDownloader class. (Superclasses receive this message before their subclasses. -- via https://developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Classes/NSObject_Class/Reference/Reference.html)